1. Field of the Invention
This invention relates generally to a method and reagent composition for simultaneous determination of at least two analytes in water samples with a single stable reagent composition containing at least two colorimetric reagents and auxiliary reagents such as buffer and masking reagent. The reagent composition can be formulated to have multiple functions including (1) clearing the deposition in the fluidic system, (2) pH buffering, and (3) acting as an auxiliary reagent to assist other analyte analysis that uses other reagents delivered within the same fluidic system.
2. Description of Related Art
Water is used in a number of industrial water systems such as cooling and boiler water systems. Municipal or untreated water contains impurities that can affect heat transfer, fluid flow, or cause corrosion of system equipment. For example, metal cations such as calcium, magnesium, barium and sodium are often present in untreated water. When the water contains an excess of these impurities, precipitates can form on equipment surfaces in the form of scales or deposits. The presence of these scales or deposits adversely affects the rate of heat transfer, and therefore the efficiency of the system. Furthermore, the cleaning or removal of such scales or deposits is expensive and burdensome because it typically requires a shutdown of the system. Accordingly, before the water is utilized for cooling or steam purposes, it is desirably treated with appropriate chemicals in order to inhibit scale formation.
It is known, for example, to add anionic water-soluble polymers to the water. One particularly useful water-soluble polymer is HPS-I (polymer of acrylic acid/1-allyoxy, 2-hydroxypropylsulfonate), although other water-soluble polymers such as AEC (polyepoxysuccinic acid) and APES (ammonium allylpolyethoxy sulfate) are in use as well. However, the employment of water-soluble polymers in industrial water systems presents its own set of problems because the concentration of the polymers in the water must be carefully monitored. For example, if too little of the polymer is employed, scaling and deposition will occur. In contrast, if too high a concentration of the polymer is employed, the cost/performance efficiency of the system is adversely affected. Additionally, chlorine is used to prevent biofilm formation in the tower. As with other methods of chemically treating aqueous systems, there is an optimal concentration of treatment chemicals that should be maintained. Monitoring and control of the industrial water chemistry is essential for maintaining proper performance and prolonging the life of the cooling tower and associated equipment.
Thus, it is understood that it is necessary to measure concentrations of multiple chemical and biological species in the industrial water, such as free chlorine, total chlorine, HPSI, and phosphate. Additionally, the pH of the water is controlled. Typically, operators rely on colorimetric analyzers based on known wet chemical analysis methods to monitor and control the water chemistry. For example, there are several colorimetric methods for determination of polyelectrolytes using dyes. One example is U.S. Pat. No. 6,214,627 issued to Ciota et al. In addition, there is a Hach polyacrylic acid method that uses iron thiocyanate chelation to detect calibration based on polyacrylic acid. Generally, these methods require a complicated, multi-step operation procedure and are difficult to carry out in the field. Other methods, such as the one disclosed in U.S. Pat. No. 5,958,778 issued to Johnson et al., use luminol-tagged polymers in combination with fluorescent or chemiluminescent detection techniques to monitor the industrial waters.
U.S. Pat. No. 5,972,713 discloses a method for determining total chlorine in a water sample using N-sulfoalkyl 3,3′,5,5′-tetramethylbenzidine (TMB-NSA). The total chlorine concentration is visually determined by changes in the color and hue of the test solution. U.S. patent application Ser. No. 11/523,021 discloses a method for determining residual chlorine in a water sample by a kit using TMB-NSA in a composition containing 3.5% sulfuric acid and alcohol to prevent the TMB-NSA from being crystallized and separating from the solution. In other colorimetric analyzers, a reagent is used for the determination of a single analyte, such as in the vanadomolybdate-based method for phosphate detection. It is seen that in most commercially available analyzers, at least one separate reagent is usually required for the determination of each analyte being measured. Previously, analyzers that use only a single reagent to determine multiple-analyte concentrations in the industrial environment have not been available.
One advantage of using a single reagent to determine multiple analyte concentrations is that the cost associated with analyzing two species is essentially the same as for a single species. Reducing the number of reagents typically required by the conventional online colorimetric analyzer also would improve instrument reliability because the number of reagent pumps and other fluidic components could be reduced. Moreover, the cost associated with reagent production, storage, transportation, and service may be reduced. Since the auxiliary reagents such as buffer are shared, liquid waste generated by an analyte using a combined reagent formulation of multiple analytes is also reduced.
Thus, there exists a strong need for simplified sensors and test methods that can easily be used to determine the concentration of multiple analytes, such as anionic polymer, phosphate, free chlorine, and total chlorine, and measure pH, using a single reagent in aqueous systems with high reproducibility, decreased response to interferences, and enhanced stability.